Unknown Earth: Why does Earth have plate tectonics?

Without plate tectonics our planet would be a very different place. The constant recycling of the Earth’s crust provides us with a stable climate, mineral and oil deposits and oceans with a life-sustaining balance of chemicals. It even gives evolution a kick every few hundred million years.

Earth is the only planet we know of that has plate tectonics. So what went right? Models have shown that for plate tectonics to get going a planet has to be just the right size&colon; too small and its lithosphere – the solid part of the crust and upper mantle – will be too thick. Too big and its powerful gravitational field squeezes any plates together, holding them tightly in place. The conditions also have to be just right&colon; the rocks making up the planet should be not too hot, not too cold, not too wet and not too dry.

For plate tectonics to get going conditions have to be just right

Yet even if these conditions are met there is one more crucial factor that needs to be introduced. Somehow the lithosphere has to be cracked in such a way that one piece will dive down beneath the other. Today we see this process, known as “subduction”, at the rim of many ocean basins, as cold, dense ocean floor slides under the more buoyant continental crust and dives into the mantle.

However, early Earth was much warmer than it is today, and instead of having a brittle outer crust it had a sticky kind …